The present invention relates to harvesting apparatus, such as combines, and particularly to a muffler system for such combines that effectively increases engine horsepower in operation.
Agricultural combines, such as disclosed in U.S. Pat. No. 6,257,977 are used to harvest crops in the field. However, there are times when such combines must be transported or driven on roads to reach the field or to return from the field. Some regulatory bodies have established noise restrictions for utility vehicles that travel on public roads. The xe2x80x9cdrive-by noise limitationsxe2x80x9d imposed by TueV and other European regulatory agencies are stringent. As the engine size and power level requirements increase, it becomes more difficult to meet these restrictions.
One source of noise emanating from a vehicle is the exhaust noise. Exhaust noise is usually attenuated by a muffler on the exhaust pipe. Normally, the noise attenuation capability of a muffler is directly proportional to its flow restriction. Flow restriction is typically measured as back pressure. Increased exhaust noise attenuation typically results in increased back pressure at the engine exhaust manifold which limits the available power from the engine.
Increased exhaust back pressure typically results in decreased available engine power, decreased fuel economy and possibly decreased turbocharger durability.
The present inventors have recognized that maximum power requirement for a combine does not occur in a road transport situation where the drive-by noise regulation must be restricted. The maximum power requirement occurs in the field. For transport on the road, the power requirement would be less than three quarters of the maximum rated power, the engine speed can be reduced, and the corresponding exhaust flows are much less than maximum flows. The present inventors have recognized that a muffler can be sized to meet these limited exhaust flows for noise attenuation requirements for road transport, but that such muffler would be too restrictive for full power operation in the field.
The present inventors have recognized that it would be desirable to develop a muffler system that reduces noise to acceptable levels during road transport, without imposing excessive back pressure limitations on the engine when operated in the field.
The present invention provides a bypass for an exhaust system for a utility vehicle, such as a combine, that, when substantially closed, would provide maximum noise attenuation for road transport, i.e., relatively high back pressure, and then, when substantially open, would provide a reduced flow restriction, i.e., relatively low back pressure, for full power, field operation.
The invention provides a bypass flow path in an exhaust pipe located upstream of a primary muffler. A diaphragm can be provided to manipulate a damper which acts to close the exhaust flow to the primary muffler and open the bypass to an exhaust pipe to effectively bypass the primary muffler, for field use of the utility vehicle. The system can be configured to entirely bypass the primary muffler and entirely route exhaust gases through the bypass or can be a system which bypasses a portion of the flow to effectively reduce back pressure while still maintaining some flow through the primary muffler. This would reduce the level of noise while still reducing back pressure to some extent. Additionally, the system could be configured to bypass exhaust gas from the primary, more restrictive muffler, to allow flow either entirely or proportionally to a less restrictive secondary muffler. Alternatively, the system could be configured such that the secondary muffler is not necessarily less restrictive, but the combined flow path through both primary and secondary mufflers is significantly less restrictive than through the primary muffler alone.
The amount of flow directed through the bypass would be dependent on the damper position. The damper position can be controlled by a diaphragm subject to positive air pressure delivered through an air line from the intake manifold of the engine, the air pressure being dependent on engine load for a turbocharged engine. Alternately, for a normally aspirated engine, intake manifold vacuum could be used to move the diaphragm. A solenoid valve can be inserted in the air line for more precise control. The solenoid valve can be controlled by a controller, preferably an electronic control unit of the vehicle. The degree of modulation of the damper could be controlled by the electronic control unit to be proportional to power requirements of the combine. When power requirements are low, all of the exhaust gases can be passed through the primary muffler. When power requirements are increased, progressively increasing amounts of exhaust gases can be bypassed by the opening of the damper, through the bypass flow path. Thus, even in the field where road noise restrictions are not applicable, a maximum amount of noise attenuation is achieved corresponding to the power demand.
The positioning of the damper can be undertaken in different ways. For example, the damper can be manually positioned by a lever and push/pull cable located in the vehicle cab and extending to the damper. Alternately, a solenoid valve can be signal connected to a manual selection switch and supplied with pressurized air, or vacuum, to manually control air pressure on the diaphragm that is connected to the damper. Alternately, the damper could be spring loaded to urge the bypass closed but which would be urged open by increasing back pressure. Alternately, an electrical switch could be triggered by an operator to open the bypass damper by use of a motorized screw thread actuator or stepper motor.
The bypass system could be electronically deactivated when the combine is placed in a higher gear used only for road travel, i.e., forcing all exhaust gas through the primary muffler. This would ensure compliance with road noise restrictions.
Numerous other advantages and features of the present invention will become readily apparent from the following detailed description of the invention and the embodiments thereof, from the claims and from the accompanying drawings.